Various toys having combined rotational motion about a horizontal axis and a translational motion in a vertical direction have been developed. One type of such toy is commonly referred to as a yo-yo. This toy has also been referred to as a return top; quiz; Prince of Wales' toy; disc, Coblenz, Incroyable; Bandalore; or emigrette. According to the Patent Office classification, a yo-yo is a tethered aerial top. A yo-yo consists of a single axle having two parallel positioned discs centrally connected to the axle. A string is connected to the axle between the discs at one end and is held in the user's hand at the other end. The string is wrapped around the axle by the user and the yo-yo is then forced downward. Upon being forced downward, the string unwinds thereby providing a rotational momentum to the discs. Once the string has been completely unwound, the rotational momentum of the discs continues to exist, thus causing the string to be rewound around the axle as it travels upward vertically toward the user's hand. The conventional structure of this yo-yo is disclosed within U.S. Pat. No. 3,263,361 to Bowden, and U.S. Pat. No. 3,256,635 to Radovan.
In another variation of the yo-yo, the string is not actually secured to, or anchored to, the axle; rather, it is looped about the axle somewhat loosely, allowing the yo-yo body to spin freely in the looped string. Such rotational motion of a yo-yo, unaccompanied by translational motion along the string direction, is referred to as "sleeping". The sleeping yo-yo can be withdrawn from its sleep by jerking the string, or alternatively, by relaxing the tension in the string. The conventional sleeper-type yo-yo is discussed in the specification of Stivers and Ennis, U.S. Pat. No. 2,629,202. Another mechanism for allowing the yo-yo to sleep, but which does not involve a looped string, is discussed in Isaacson, U.S. Pat. No. 3,175,326. Isaacson's device involves an axle which is rotatably supported in a ball-bearing system.
The conventional yo-yo structure as described above has achieved tremendous success in the past as an entertaining toy. Furthermore, certain modifications of that conventional yo-yo such as that disclosed within Bowden or Isaacson may have achieved success as entertaining toys. However, the conventional yo-yo structure has a pronounced limitation when used by inexperienced or younger operators. The limitation is apparent to even the most casual observer and resides in the difficulty of maintaining the balance or equilibrium of the toy during use. The inability of the inexperienced user to maintain this balance results in a wobbling and precessional motion of the yo-yo during operation. The operator loses control of the yo-yo when the balance of the toy is disturbed, thus causing the yo-yo to slow its rotational motion and thereby lose its ability to maintain vertical translational motion.
An examination of the prior art in this field shows that it is comprised of yo-yo toys of conventional structure, conventional yo-yos with slight aesthetic modifications, yo-yos whose structure has been modified with the intent of providing improved stability, and yo-yos whose conventional structure has been modified with the intent of providing additional versatility and function.
One of the features which is repeatedly emphasized as being of value in the dynamics of yo-yo motion is an increased moment of inertia for the yo-yo body. Assuming a fixed mass for the yo-yo body, this is achieved by distributing as much of the mass as possible close to the outer rim of the yo-yo. This topic is discussed in a number of U.S. Pat. Nos. such as 59,745 to Haven and Hettrich; 668,829 to Boehme; 3,175,326 to Isaacson; and 3,805,443 to Duncan. Such inertial rings or flywheels are found on a number of commercially available yo-yos.
On the other hand, the smaller the moment of inertia of a yo-yo body, the greater the angular velocity which can be imparted to it by a given impulse or torque. This increases the `speed` of a particular yo-yo, as discussed by Stivers and Ennis in U.S. Pat. No. 2,629,202.
In the context of this specification, the term "stability of yo-yo" is intended to mean the tendency of the yo-yo axle to remain in horizontal alignment, and its tendency to return to this alignment if it is displaced therefrom by some means. The term "stability of yo-yo" also refers to the facility with which proper yo-yo operation can be re-established after it experiences severe wobbling or precessional rotation; the greater the stability of the yo-yo, the easier it is to re-establish proper operation after it encounters difficulty. "Stability of yo-yo" also refers to its tendency to resist engaging in precessional rotation.
In the specification and claims of this application, the term "twist-resistant string" means that the string offers a significant barrier or opposition to twisting about the longitudinal axis of the string compared to conventional yo-yo strings which have been used on commercial yo-yos up to the present time. Of course, in order to be useful for a yo-yo, such a twist-resistant string must be flexible about axes transverse to the longitudinal axis of the string in order that the string may wind about the yo-yo axle.
As an indication of the increased versatility of the yo-yo presented herein, the user will find that the yo-yo can be handled quite roughly during its operation, and still, the user continues to retain control of its motion. The ability of the twist-resistant string to resist twisting about its longitudinal axis hinders the yo-yo from engaging in precessional rotation and also facilitates the yo-yo in recovering from precessional motion when such does occur.